The aim of this study was to define an other cause of idiopathic constipation with a mathematic automatic classification Fifty patients were studied by colonic transit time, anorectal manometry and defecography. Three classical causes were found: 12 patients had hypertonic upper anal pressure; 8 patients had abnormal rectonanal inhibitory reflex and 12 patients had anatomic conditions reducing stool frequencies Automatic mathematic classification coming from optimised bowls technic has led to the characterization of a new cause. Eight young women (mean age 33 years) with hypertonic striated pelvic muscles on straining were identified. Three items were significantly different: defect of sphincteric relaxation without high sphincteric pressure; closure or non opening anorectal angle, hypertonic levator ani on straining. There was a significant high frequency (p less than 0.05) of urinary disorders in this new group. All abnormalities occurred during defecation. This group can be studied with other methods: balloon expulsion, anal electromyography. Clinical identity with urinary pathology may be explained by common neurologic disorders of pelvic striated muscle innervation.